1. Field of the Invention
The present invention relates to a method for manufacturing active matrix liquid crystal displays ("AMLCD"), and to the structure of AMLCDs manufactured by such a method.
2. Discussion of the Related Art
AMLCDs comprise active elements such as thin film transistors ("TFT") as switching devices for driving and controlling each pixel of the display.
As shown in FIG. 1A, in a conventional AMLCD including an array of TFTs, substantially rectangular pixel electrodes 47 are closely arranged in rows and columns on a transparent glass substrate. Gate bus lines (address lines) 13 are respectively formed closely along the rows of the pixel electrodes 47 and source bus lines (data lines) 14 are respectively formed closely along the columns of the pixel electrodes.
Referring to FIG. 1B, a plan view showing an enlargement of a single pixel of the AMLCD shown in FIG. 1A, gate bus lines 13 having gate electrode extensions 33 are formed on a transparent glass substrate 31 (FIG. 2A). An insulating layer 35 (FIG. 2B) covers the gate bus lines 13 and the gate electrodes 33, and a plurality of parallel source bus lines 14 are provided on the insulating layer extending perpendicular to gate bus lines 13. Near each gate bus line 13 and source bus line 14 intersection, a semiconductor layer 37 (FIG. 2B) is formed on the insulating layer covering the gate bus lines and the gate electrodes. Spaced source and drain electrodes, 43a and 43b respectively FIG. 2D), are formed opposite one another on the semiconductor layer. In this manner, TFTs as active elements are formed.
A manufacturing process of a conventional AMLCD is described below with reference to FIGS. 2A to 2E, showing cross-sectional views taken along a line 2--2 of FIG. 1B.
A gate electrode 33 (extension of a gate bus line 13) is formed on a transparent glass substrate 31 by depositing and patterning a first metal layer (FIG. 2A). A first insulating layer (a gate insulating layer) 35 made of SiN.sub.x, a semiconductor layer 37 made of a-Si, and a second insulating layer made of SiN.sub.x are then successively deposited on the entire surface of the substrate.
As shown in FIG. 2B, an etch-stopper 40 is formed by patterning the second insulating layer, and an impurity doped semiconductor layer 39 including n.sup.+ a-Si is then deposited over the entire substrate and patterned together with the semiconductor layer 37 (FIG. 2C).
A second metal layer 43 is next deposited on the entire surface of the substrate, which is then patterned to form a bus line, a source electrode 43a branching out from the source bus line, and a drain electrode 43b. Next, an exposed portion of the impurity doped semiconductor layer 39 is etched using the source and drain electrodes as masks, as shown in FIG. 2D.
An insulating passivation layer 45 is then formed by depositing another Si-nitride layer over the first insulating layer and the source and drain electrodes. Then a contact hole is formed by etching the insulating passivation layer 45. An ITO layer is sputter deposited on the insulating passivation layer 45. The ITO layer is patterned to form a pixel electrode 47, which is electrically connected to the drain electrode 43b through a contact hole (FIG. 2E).
This conventional process of manufacturing the TFTs is very complicated. Moreover, it takes a great deal of time to pattern the various layers of the AMLCD because the mask must be aligned precisely, and photo-resists must be coated and developed for each mask step. Further, the manufacturing yield is low.